1. Field of the Invention
The present invention relates to a droplet ejection head such as an ink jet recording head, and a method for manufacturing the same.
2. Description of the Related Art
A droplet ejection head is used in a wide range of applications such as a printer, an apparatus for manufacturing a display component and a medical inhaler, and is expected to be applied to many industries in the future as well. As a droplet ejection head used in a printer, an ink jet recording head is used which can eject a droplet with high density and high accuracy.
The ink jet recording head has a head structure such as electric wires and an ejection orifice for ejecting an ink droplet therethrough provided on a substrate made of silicon or the like. The head structure includes an ink flow channel through which ink flows on a substrate, a flow channel member for surrounding the ink flow channel, an orifice plate provided with an ejection orifice and an energy-generating element for imparting energy to the ink and thereby ejecting an ink droplet from the ejection orifice. The substrate having such a head structure provided thereon is hereinafter referred to as a head substrate.
The energy-generating element includes an electrothermal transducer (heater element) for boiling a liquid, and a piezo element for imparting a pressure to a liquid by virtue of change in volume. The flow channel member and the orifice plate include those prepared by patterning an organic thin film or an inorganic thin film using a photolithographic process.
To manufacture an ink jet recording head, a method is commonly used which involves laminating an orifice plate with a head substrate having a flow channel member formed thereon through a flow channel member. Japanese Patent Application Laid-Open No. H11-334079 and Japanese Patent Application Laid-Open No. 2001-18392 are mentioned as prior art documents.
When the orifice plate is laminated with the head substrate, at least one of the flow channel member and the orifice plate is formed from a material having adhesiveness, and both the orifice plate and head substrate are bonded to each other by a pressure bonding method. FIGS. 8A and 8B illustrate a sectional view for describing a conventional process for manufacturing an ink jet recording head. As in FIG. 8A, an orifice plate 2 having the ejection orifice 4 formed thereon is aligned with a head substrate 30 having a flow channel member 3 and an energy-generating element 7 formed on a substrate 1, and in FIG. 8B, the orifice plate 2 is pressure-bonded to the head substrate 30 with a thermocompression bonding machine or the like.
In addition, an adhesive may be applied onto the surface of the flow channel member 3 or the orifice plate 2, and then the adhesive may be caused to develop its adhesiveness by heating or UV radiation, and the orifice plate 2 and flow channel member 3 may be bonded to each other under pressure applied. Furthermore, an elastic body member, such as rubber, may be inserted into between the pressure bonding part of the thermocompression bonding machine and a sample (orifice plate 2 and head substrate 30) to enhance the uniformity of pressure bonding.
The thermocompression bonding operation shown in FIGS. 8A and 8B is conducted for the purpose of bonding the orifice plate 2 with the flow channel member 3. Process conditions in pressure bonding include a pressure-bonding period of time, a pressure-bonding temperature and a pressure-bonding pressure. These conditions are determined according to the bonding conditions of the adhesive used.
However, in some of the ink jet recording heads manufactured by such a manufacturing method, there have been cases where the flow channel member and the orifice plate are not ideally bonded to each other and such a phenomenon occurs where the orifice plate locally protrudes toward an ejection direction. On the other hand, there also have been cases where such a phenomenon occurs where the orifice plate protrudes toward the side of the flow channel member.
If such a flexure occurs in the orifice plate, the ejection direction of the droplet occasionally results in tilting from the desired direction to which the droplet should be ideally ejected. In addition, there are cases where the ejection speed and the volume of the droplet to be ejected results in changing because the energy of the droplet necessary for ejection changes. These phenomena are crucial because of causing a print pattern failure of the printer.
Such a flexure of an orifice plate is a phenomenon which may occur also in a droplet ejection head in applications other than the printer. When this phenomenon has occurred, for instance, in the medical inhaler, in some cases, the ejection amount of the medicine to be inhaled by a patient may be changed as a result.
In addition, it is important from the viewpoint of enhancing the performance of the printer to reduce the power consumption of the ink jet recording head. In order to reduce the power consumption of the ink jet recording head, it is effective to minimize the thickness of the orifice plate to thereby reduce the fluid resistance of the ejection orifice and to lower the energy necessary for ejection. However, the orifice plate has a tendency of decreasing its rigidity as it becomes thin, and accordingly has a tendency of causing local flexure in the orifice plate when it is laminated. When the thickness of the orifice plate becomes particularly 10 μm or less, it may become difficult even to handle the orifice plate, and the plate tends to easily cause flexure or deformation.
It is also effective as another method of reducing the power consumption to reduce a gap between an energy-generating element and an ejection orifice (or, orifice plate). However, as the gap between the energy-generating element and the ejection orifice becomes smaller, the variation in the gap distances due to the flexure of the orifice plate produces a relatively large influence on the performance.
Furthermore, as is pointed out in Japanese Patent Application Laid-Open No. H11-334079, when the gap between the energy-generating element and the ejection orifice becomes smaller, there is a possibility that the orifice plate may be locally flexed or bent and may be brought into contact with the energy-generating element. If the orifice plate contacts the energy-generating element, there are cases where foaming to be caused by a heater is disturbed and there are cases where the ink thereby cannot be ejected.
Accordingly, when it is intended to make the orifice plate thinner or decrease the gap between the energy-generating element and the orifice plate, for the purpose of lowering the power consumption, the influence of the flexure of the orifice plate becomes more serious.
The causes of the above described flexure of the orifice plate may include non-uniformity of the pressure applied when the orifice plate is pressure-bonded, low flatness of the flow channel member surface and the orifice plate surface, and deformation of the orifice formed during the manufacturing thereof. The issue of flexure has been conventionally solved by enhancing the uniformity of the pressure applied to the head substrate when the head substrate is pressure-bonded, and flattening the surface to be bonded. In Japanese Patent Application Laid-Open No. 2001-18392, a method is proposed by which a joint-assisting member is provided between an orifice plate and a flow channel member and the joint-assisting member is caused to absorb unevenness on the surface of the flow channel member.
However, there is a limit even when the uniformity of the pressure-bonding pressure and the flatness of a face to be bonded are improved, and it may be difficult to enhance the yield of the head only by the above methods. It may also be difficult to provide such an effect as to suppress the flexure that may locally occur in the orifice plate when the orifice plate is simply pressure-bonded with the flow channel member as in a conventional technology.
In addition, the method of providing a joint-assisting member between the flow channel member and the orifice plate as described in Japanese Patent Application Laid-Open No. 2001-18392 is disadvantageous in terms of the cost by an additional process of using the joint-assisting member.